1. Field of the Invention
The present invention relates generally to the field of processing video information, and, more particularly, the present invention relates to an improved device and method of processing video display signals.
2. Description of the Related Art
The encoding of video signals in accordance with the image encoding standards H.261, H.263, MPEG1 as well as MPEG2 is often based on a block-oriented discrete cosine transformation (DCT). These block-oriented encoding methods, however, are not suitable for image encoding methods that are no longer based on rectangular blocks. For example, subjects from an image may be segmented and the segments of the image are encoded. These methods are referred to as region-based or subject-based image encoding methods. A segmenting of digital images thereby takes place according to the subjects occurring in the scene. A separate encoding of these segmented subjects is implemented instead of encoding the image blocks as in block-based image encoding methods. The encoding thereby usually is accomplished by modeling the segmented subjects and subsequent transmission of the modeling parameters for these segmented subjects.
After transmitting the image information from a transmitter to a receiver, the individual subjects of the image are in turn reconstructed in the receiver on the basis of the transmitted modeling parameters.
One possibility for modeling the subjects is a series development of the image function according to a set of suitably selected basic functions. The modeling parameters then correspond to the development coefficients of these image functions. Such a modeling of the image is the basis for transformation encoding. When individual, arbitrarily bounded subjects of the image are to be encoded, a transformation for segments with arbitrary, usually not convex bounds is required. Two basic approaches have previously existed for such a transformation.
In the method described in M. Gilge, T. Engelhardt and R. Mehlan, Coding of Arbitrarily Shaped Image Segments Based on a Generalized Orthogonal Transform, Signal Processing: Image Communication 1, 00. 153-180, October 1989, a given image segment is first embedded in a circumscribing rectangle having the smallest possible dimensions. A discrete cosine transformation (DCT) that is completely specified by the basic functions of the transformation can be recited for this rectangle. In order to match this transformation to the segment shape, the basic functions defined for the rectangle are successively orthogonalized with respect to the shape of the segment. The resulting orthogonal, shape-dependent basic functions then form the segment-matched transformation that is desired.
One disadvantage of this approach is that there is a tremendous demand for calculating capacity and memory for implementing this method. Further, with this known method no reliable statements can be made about the resultant transformation for data compression, since the transformation is essentially dependent on the orthogonalization sequence and, thus, on the specific implementation.
T. Sikora and Bela Makai, Shape-adaptive DCT for generic coding of video, IEEE Trans. Circuits and Systems for Video Technology 5, pp. 59-62, February 1995 describes a method wherein the given image segment is separately transformed according to rows and columns. To that end, all rows of the image segment are first aligned on the left and successively subjected to a one-dimensional horizontal transformation whose transformation length respectively corresponds to the number of picture elements in the corresponding row. The resultant coefficients are subsequently transformed a second time in vertical direction.
This method has the disadvantage that correlations of the brightness values for the picture elements (similarities of the picture elements) cannot be fully exploited due to resorting of the picture elements.
For improving this method T. Sikora, S. Bauer and Bela Makai, Efficiency of Shape-Adaptive 2-D Transforms For Coding of Arbitrary Shaped Image Segments, IEEE Trans. Circuits and Systems for Video Technology 5, pp. 254-258, June 1995 [3] describes a method wherein a transformation for convex image segment shapes adapted to a simple image model is implemented. However, only image segment shapes that exhibit no interruptions (holes) upon traversal of rows or columns are allowed.
In the above-described, known methods due to the variable transformation length, standard transformation methods or, respectively, standard modules can no longer be utilized for implementation of the transformation which is undesirable.
Standard image transformation methods are known, for example, from R. J. Clarke, Transform Coding of Images, Academic Press, London, pp. 72-134, 1985. Because standard image transformation methods can no longer be applied, substantial costs arise for encoding units that work according to the known, above-described methods.
The present invention specifies a method for processing picture elements of an image segment with an arbitrary shape that exhibits image segments of a target image segment shape. Standard image transformation methods and encoding devices are compatible and can continue to be utilized for implementation thereof. Other objects and advantages of the present invention will be apparent form the following summary and detailed description of the preferred embodiments when viewed in light of the drawings.